The field of this invention is the one is which gaseous oxygen is produced by a chemical reaction. It is further distinguished in that the chemical which reacts to yield oxygen is regenerated by contacting it with air or other oxygen containing gas. Thus there is not net consumption of the chemical; the net result is that the input air is separated into an oxygen enriched gas and an oxygen depleted gas by the input of heat.
Oxygen is widely used in large amounts in various industries, predominantly in the manufacture of steel, and has the prospect of substantially greater consumption in future coal conversion and hydrogen generation processes.
The prior art of this field of invention includes U.S. Pat. Nos. 3,856,928; 3,579,292; 2,418,402; and 2,490,587. Numerous oxygen acceptors have been identified, including BaO, Na.sub.2 MnO.sub.4, CuCl.sub.2, SrO, and Hg. The attrubute of chemical air separation processes as a class is that the high pressure air which undergoes reaction and thereby loses part of its oxygen is still at high pressure after the reaction. Therefore it can be expanded through a turboexpander, recovering most or all of its compression energy. In contrast, in cyrogenic processes the air must at least partly be expanded through an orifice to develop the desired cooling effect, thereby expending the compression energy. Liquefaction processes accordingly consume electrical energy at the relatively high rate of 0.35 kWhr (1.2 .times. 10.sup.6 J) per kg O.sub.2 produced, which is equivalent to 1 thermal kWhr per kg or 27.5 kcal/mole O.sub.2. Nevertheless, the liquefaction process has been superior to prior art chemical separation processes for various reasons. All prior art processes have involved either an acceptor or an oxidized acceptor or both which are present in the solid state. This has made circulation of the acceptor composition difficult, and therefore most processes have been batch mode. Most batch mode processes have involved large pressure differences between the oxidation and decomposition parts of the cycle, and therefore have suffered from excessive vent and purge losses. Some processes have attempted to minimize this pressure difference by conducting the decomposition reaction at a higher temperature than the oxidation reaction. This imposes a large heat requirement: not only does the sensible heat of the acceptor have to be furnished, but the full endothermic heat requirement of the decomposition reaction must also be supplied. Together they add up to substantially more than the 27.5 kcal/mole needed for liquefaction. The same considerations have hindered the few continuous processes disclosed; the large pressure difference operating mode has made acceptor circulation extremely difficult (virtually impossible for fluidized beds), whereas the operating mode yielding more equal pressures has suffered from excessive energy requirements. Other problems with the prior art processes are that some of them result in unacceptable amounts of impurities in the product gas, e.g. chlorine or mercury, and some result in an unacceptable loss rate of the acceptor, due to chemical breakdown, chemical inactivation, or other possible causes.